Collaborative Research: Filling in the Central Himalayan Seismic Gap: A Structural, Neotectonic, and Paleoseismic Investigation of the Western Nepal Fault System

合作研究：填补喜马拉雅中部地震间隙：尼泊尔西部断层系的构造、新构造和古地震研究

• 批准号: 1827870
• 负责人: Sean Bemis
• 金额: $ 20.31万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-15 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1827870&HistoricalAwards=false
• 关键词: Collaborative; Research; Filling; Central; Himalayan

The 2015 Gorkha Mw 7.8 earthquake, which caused 9,000 fatalities, resulted from rupture along a megathrust - the Main Himalayan thrust - where the Indian sub-continent subducts beneath deformed Himalayan belt and the Asian continent. Most megathrust fault systems, where one tectonic plate is being forced underneath another tectonic plate, occur deep beneath the world's oceans where observations are limited due to difficult submarine access. These systems produce the largest recorded earthquakes in the world and typically consist of a primary fault and additional splay faults that work together to accommodate collision between the tectonic plates. A recently discovered complex fault system west of the Gorkha epicentral region, the Western Nepal Fault System (WNFS), appears to play a major role in accommodating the Himalayan collision and poses a major seismic hazard for a large region of Nepal. This project will document the long-term rate of motion, determine the timing and location of prehistoric earthquakes, and map out the full extent of the WNFS. The data will be used to develop constraints on the seismic hazard exposure of regional populations and provide recommendations for low-cost, sustainable, and culturally sensitive earthquake risk mitigation strategies. The project would advance other desired societal outcomes such as full participation of women in STEM, increased public scientific literacy and public engagement with STEM through participation in local public outreach activities, development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training, and fostering international collaboration.Geologic and geophysical observations have long shown that areas of oblique plate convergence tend to form slip partitioned systems, where the basal megathrust accommodates margin-perpendicular convergence, and a strike-slip splay or backarc fault accommodates margin-parallel motion. Given the curvature of most convergent margins, convergence obliquity often varies along strike, becoming zero at some point. However, because these zones are usually inaccessible in offshore subduction zones, the kinematics and earthquake cycle behavior of these splay faults are poorly known. This project targets the newly discovered Western Nepal Fault System as a major, subaerial, well-exposed splay fault system within the Himalayan thrust wedge that appears to transfer dextral strain from the Karakoram Fault in the obliquely convergent northwest Himalayan backarc to the central Himalayan forearc where convergence is primarily margin-normal. The objective of this project is to test multiple working hypotheses that use the deformation patterns of the WNFS to constrain models of fault segmentation and linkage for regional slip-partitioning and splay faulting models: (1) strong strain partitioning hypothesis in which the WNFS is a well-connected system of active faults that transfer slip from the Karakoram- Gurla Mandhata/Humla fault system in the northwest, across the thrust wedge, and branches with the Main Frontal Thrust at the front of the wedge; (2) weak strain partitioning hypothesis in which the WNFS is a collection of disconnected faults that broadly accommodate arc-parallel strike-slip faulting and northwest translation of the Himalayan arc sliver; and (3) thrust faulting and oblique ramp hypothesis in which the WNFS is a collection of faults that accommodate shortening within the thrust wedge. To address these hypotheses and leverage new constraints on regional seismic hazard, the research team will carry out a three year multidisciplinary investigation consisting of three primary components: (1) structural geology, neotectonics, geomechanics, and geochronology with paleoseismology to constrain (a) the geometries and kinematics of active fault systems, (b) displacement magnitude, (c) fault slip rates, and (d) historical patterns of strain release using paleoseismology; (2) an updated probabilistic seismic hazard and risk analysis integrating the results of the geologic studies; and (3) a benefit-cost analysis of structural and non-structural vulnerability-reducing strategies at household to community scales to provide recommendations for reducing risk and promoting resilience through mitigation and recovery. The active fault mapping, slip rate, and paleoearthquake data are also fundamental components of seismic hazard analyses. Working with Nepali collaborators, the results will be used to provide updated probabilistic seismic hazard analysis and develop practical mitigation strategies for a region widely thought to be at heightened seismic risk.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

2015年戈尔卡MW 7.8地震造成了9,000人死亡，这是由于沿巨型巨星（主要喜马拉雅推力）破裂造成的 - 印度次陆上悬停在畸形的喜马拉雅腰带和亚洲大陆。大多数巨型断层系统，一个构造板被迫在另一个构造板下方被迫，出现在世界海洋之下，在世界海洋下，观察值由于难以进入潜艇的通道而受到限制。这些系统会产生世界上最大的记录地震，通常由主要断层和额外的断层组成，这些断层可以合作，以适应构造板之间的碰撞。最近发现的一个复杂的断层系统西中心地区西部尼泊尔断层系统（WNFS）似乎在适应喜马拉雅碰撞方面起着重要作用，并对尼泊尔的大部分地区构成了重大的地震危险。该项目将记录长期运动率，确定史前地震的时间和位置，并绘制WNF的全部范围。这些数据将用于开发对区域人口的地震危害暴露的限制，并为低成本，可持续和文化敏感的地震降低风险策略提供建议。该项目将通过参与当地的公共宣传活动，发展多样化的，全球竞争性的STEM劳动力的发展，通过本科生和研究生培训的发展以及促进国际合作培训的底层倾向于倾向的分配，诸如妇女的公共科学素养和公众参与度，诸如女性的全面参与，提高了公共科学素养和与STEM的公众参与，以及与STEM与STEM的公众参与，并促进国际合作型的组成部分的分配趋向于跨越的系统，该领域倾向于采取行动，该领域的分配方式倾向于，该领域的分配趋向于促进plate的分配，诸如妇女的公共科学素养和公众参与。地理位置和地球物质的分配趋向于跨越层的分配，从而提高了公共科学素养和公众参与。 Megathrust可容纳边缘 - 垂直收敛，而滑滑或后弧故障可容纳边缘并行运动。鉴于大多数收敛边缘的曲率，收敛倾斜通常会随着打击而变化，在某个时候变为零。但是，由于这些区域通常在离岸俯冲带中无法访问，因此这些散布断层的运动学和地震循环行为是鲜为人知的。该项目将新发现的西部尼泊尔断层系统定为喜马拉雅推力楔内的主要，海底，暴露良好的散布故障系统，该系统似乎是从卡拉科姆（Karakoram）断层转移到西北喜马拉雅山脉后的Karakoram断层中的右旋菌株，转移到了喜马拉雅山中部的中部前前体中，其中compergence convergence是主要的。该项目的目的是测试多个使用WNF的变形模式来限制故障细分模型和链接模型的区域滑动分区和触发断层模型的模型：（1）WNFS的强大应变分配假说，其中WNFS是一个良好的主动缺陷系统，该系统从Karakoram-gurla andla andla and and and and andla unla themant andla unla andla andla and and and themant andla unah andla and and yra and yra and yraha thau thanf推力楔子，并在楔形前的主要额叶上推进分支； （2）弱应变分区假设，其中WNF是断开断层的集合，该断层广泛地适应了喜马拉雅弧sliver的Arc平行滑移断层和西北翻译； （3）推力断层和倾斜的坡道假说，其中WNF是一系列故障，可容纳推力楔内的缩短。 To address these hypotheses and leverage new constraints on regional seismic hazard, the research team will carry out a three year multidisciplinary investigation consisting of three primary components: (1) structural geology, neotectonics, geomechanics, and geochronology with paleoseismology to constrain (a) the geometries and kinematics of active fault systems, (b) displacement magnitude, (c) fault slip rates, and （d）使用古介质学的释放菌株的历史模式； （2）整合地质研究结果的更新的概率地震危害和风险分析； （3）对家庭规模降低结构性和非结构性脆弱性策略的福利成本分析，以提供建议，以通过缓解和恢复来降低风险并促进韧性。主动故障映射，滑动速率和古夸张数据也是地震危险分析的基本组成部分。与尼泊尔合作者合作，结果将用于提供最新的概率地震危害分析，并为一个被认为处于高度地震风险的地区制定实用的缓解策略。该奖项反映了NSF的法定任务，并被认为是通过基金会的智力优点和广泛的影响来评估的，并被认为是值得通过评估的支持。